Field of the invention
The present invention relates to a heat treatment method and a heat treatment apparatus, for irradiating a thin-plated precision electronic substrate (hereinafter referred to as simply “substrate”) such as a semiconductor wafer with a flash of light to heat the substrate.
Description of the Background Art
In a manufacturing process of semiconductor devices, flash lamp annealing (FLA) for heating a semiconductor wafer for an extremely short time has been paid attention. The flash lamp annealing is a heat treatment technology for irradiating a surface of a semiconductor wafer with a flash of light by using a xenon flash lamp (hereinafter when referred to as simply a “flash lamp”, it means a xenon flash lamp) to increase temperature of only the surface of the semiconductor wafer in an extremely short time (milliseconds or less).
The xenon flash lamp has an emission spectroscopy distribution radiation from an ultraviolet part to a near-infrared part, and has a wave length that is shorter than that of a conventional halogen lamp, and that almost coincides with that of a fundamental absorption band of a semiconductor wafer made of silicon. This causes transmitted light to decrease when the xenon flash lamp irradiates a semiconductor wafer with a flash of light, so that temperature of the semiconductor wafer can be rapidly increased. It is also found that flash irradiation for an extremely short time of milliseconds or less enables only near a surface of a semiconductor wafer to be selectively increased in temperature.
This kind of flash lamp annealing is used for treatment requiring heating for an extremely short time, such as typically activation of impurities implanted into a semiconductor wafer. When a flash lamp irradiates a surface of a semiconductor wafer, into which impurities are implanted by an ion implantation method, with a flash of light, temperature of the surface of the semiconductor wafer can be increased to an activation temperature for only an extremely short time, whereby only impurity activation can be performed without diffusing the impurities deeply.
A flash lamp emits a flash of light that is an optical pulse with an extremely short irradiation time and high intensity, so that when the flash of light is emitted, a structure and a gas in a chamber in which a semiconductor wafer is accommodated are rapidly heated to cause instantaneous gas expansion followed by shrinkage. As a result, particles curl up and fly in the chamber. US2005/0047767 discloses a technique of intentionally irradiating an empty chamber in which no semiconductor wafer is accommodated with a flash of light multiple times to cause particles to fly in the chamber by using the above-mentioned phenomenon when a flash of light is emitted, and then forming a flow of nitrogen gas in the chamber to discharge the particles to the outside of the chamber.
Unfortunately, the phenomenon, in which particles curl up in a chamber when a flash of light is emitted, also occurs when flash heating is applied to a semiconductor wafer to be treated. When particles as described above are attached to a surface of a semiconductor wafer, the particles cause a problem in that the semiconductor wafer is contaminated.